Because the utilisation of the reactant concerned is known, the flow rate of said reactant can be determined. This is important for diverse applications.
In particular, a method of this type can be used to determine the relationship between the flow rates in the various cells of a stack of fuel cells.
After all, in the case of a cell stack it is important that all cells make approximately the same contribution to the total voltage. If one of the cells functions less well, this immediately has an effect on the entire stack, in particular if, as is customary, it is a matter of electric current in a serial circuit.
In the case of the production of electrochemical cells, and more particularly fuel cells, on an industrial scale, the flow resistance of the separator plates and/or other constructions for feeding in and removing the reactants will be different, inter alia because of manufacturing tolerances, creep and corrosion. If reactants are introduced in parallel into a cell stack, then, with the manifolding used, all the gas introduced will be fed over the first cell and that portion for said first cell will be removed at the latter, all the gas minus the gas removed for the first cell will be fed over the second cell, etc. The same applies for the outlet side. This means that there are always different flow conditions. Because in the case of a serial circuit the electric current which passes through each cell is the same, there will be more polarisation in a cell where an inadmissible restriction in the flow occurs, as a result of which the cell voltage falls.
Methods are proposed in the prior art for determining the hydraulic resistance per cell using conventional flow meters at the output for reactants at the anode and the cathode and measuring the pressure drop and in this way investigating whether inadmissible deviations between cells occur during production or operation.
A method of this type is suitable only for a single cell and is unsuitable for measuring during operation of a fuel cell stack. The effect of, for example, manifolding on cells cannot be measured by this method. This applies in particular if a fuel cell stack is operated at higher temperatures or under other conditions which deviate from ambient conditions. This means that a measurement under operating conditions is not possible and, therefore, does not yield results which are adequately in accord with the operating conditions.
Furthermore, the measurement described above is complex. As a result, during mass production of electrochemical cells one will not be readily inclined to conduct such measurement as standard for every cell.